Latent electrostatic image development

ABSTRACT

METHOD FOR DEVELOPMENT OF A LATENT ELECTROSTATIC IMAGE EMPLOYING A DONOR MEMBER ADAPTED TO RETAIN TONER ON ITS SURFACE AND HAVING A NUMBER OF PROCESSING STATIONS ARRANGED AROUND ITS PERIPHERY THE DONOR MEMBER HAS A CORONA-CHARGEABLE DIELECTRIC SURFACE AND IS POSITIONED SO THAT A PORTION OF ITS PERIPHERY PASSES THROUGH TONER IN A VIBRATING RESERVOIR. THE RESERVOIR IS MAINTAINED AT A POTENTIAL LOWER THAN THE CHARGED DONOR MEMBER. THE TONER IS TRIBOELECTRICALLY CHARGED IN THE VIBRATING RESERVOIR VIA A COATING ON THE INSIDE OF THE RESERVOIR CAPABLE OF SO CHARGING THE TONER AND SAID TONER IS ATTRACTED TO THE DIELECTRIC SURFACE OF THE DONOR WHICH IS CORONA CHARGED OPPOSITELY TO THAT OF THE TONER.

DCC. 26, Y J. MAKSYMMK ETAL LATENT ELECTROSTATIC IMAGE DEVELOPMENT Filed Jan. 6, 1971 I I I I I I I I'"'v'"'I' INVENTORfi JOHN MAKSYMIAK 2 JA ES W. SMITH A T TORNE Y US. Cl. 11717.5 2 Claims ABSTRACT OF THE DISCLOSURE Method for development of a latent electrostatic image employing a donor member adapted to retain toner on its surface and having a number of processing stations arranged around its periphery The donor member has a corona-chargeable dielectric surface and is positioned so that a portion of its periphery passes through toner in a vibrating reservoir. The reservoir is maintained at a potential lower than the charged donor member. The toner is triboelectrically charged in the vibrating reservoir via a coating on the inside of the reservoir capable of so charging the toner and said toner is attracted to the dielectric surface of the donor which is corona charged oppositely to that of the toner.

BACKGROUND OF THE INVENTION This method and apparatus relates to the development of electrostatic images and more particularly to an improved method and apparatus for xerographic development by which a toner layer is presented to a latent image for development thereof.

In the reproduction process of xerography, a photoconductive surface is charged and then exposed to a light pattern of the information to be reproduced thereby forming an electrostatic latent image on the photoconductive surface. Toner particles, which may be finely divided, pigmented, resinous material are presented to the latent image Where they are attracted to the photoconductive surface. A toner image can be fixed and made permanent on the photoconductive surface or it can be transferred to another surface where it is fixed.

One known method of developing latent electrostatic images is a process called transfer development. Transfer development broadly involves bringing a layer of toner to an imaged photoconductor where toner particles will be transferred from the layer to the image areas. In one transfer development technique, a layer of toner particles is applied to a donor member which is capable of retaining the particles on its surface and then the donor member is brought into close proximity to the surface of the photoconductor. In the closely spaced position, particles of toner in the toner layer on the donor member are attracted to the photoconductor by the electrostatic charge on the photoconductor so that development takes place. In this technique the toner particles must traverse an air gap to reach the imaged regions of the photoconductor. In two other transfer techniques the toner-laden donor actually contacts the imaged photoreceptor and no air gap is involved. In one such technique the tonere United States Patent O 3,707,389 Patented Dec. 26, 1972 laden donor is rolled in a non-slip relationship into and out of contact with the electrostatic latent image to develop image in a single rapid step. In another such technique, the toner-laden donor is skidded across the xerographic surface. Skidding the toner by as much as the width of the thinnest line will double the amount of toner available for development of a line which is perpendicular to the skid direction, and the amount of skidding can be increased to achieve greater density or greater area coverage.

It is to be noted, therefore, that the term transfer development is generic to development techniques where (1) the toner layer is out of contact with the image photoconductor and the toner particles must traverse an air gap to effect development, (2) the toner layer is brought into rolling contact with the image photoconductor to effect development, and (3) the toner layer is brought into contact with the imaged photoconductor and skidded across the image surface to effect development. Transfer development has also come to be known as touchdown development.

In a typical transfer development system, a cylindrical or endless donor member is rotated so that its surface can be presented to the moving surface of a photoconductive drum bearing an electrostatic image thereon. Positioned about the periphery of the donor member are a number of processing stations including, a donor loading station, at which toner is retained on the donor member surface; a charging station at which a uniform charge is placed on the particles of toner retained on the donor surface; a development station at which the toner particles are presented to the image photoconductor for image develop ment; and another charging station at which a neutralizing charge is placed upon the residual toner particles and at which a cleaning member removes residual toner from the peripheral surface of the donor. In this manner, a more or less continuous development process is carried out.

Among the donor members employed in the process rial. The first layer of poorly insulating material is so selected as to have a resistivity sufficiently high to accept an electrostatic charge thereby permitting electrostatic charging of the entire donor surface including the posts or dots and the areas therebetween to uniform potential. However, the resistivity of the first dielectric is sufiiciently low so that by the time the donor member has moved from the point of charging into the toner loading mechanism, substantially all of the electrostatic charge on this portion has been lost, i.e. discharged to the condutive backing. This then leaves the posts or dots uniformly charged to a desired potential by virtue of its considerably higher resistivity. When a donor member of this construction comes into contact with a suitably charged mass of toner particles, the toner particles will be attracted to the post or dot areas and the regions between the dots or posts will be free of toner particles. The donor member in this manner is loaded with toner for presentation to the development region of the system.

A shortcoming of this technique is the fact that considerable expense, time and effort is involved in constructing a donor member of this configuration. The art of latent electrostatic image development and in particular transfer development would be significantly advanced if the donor member and technique of loading the donor could be simplified.

Accordingly, it is an object of the invention to improve donor member apparatus for developing latent electrostatic images.

It is a further object of the invention to improve apparatus for accomplishing transfer development of xerographic images.

It is still a further object of the invention to simplify the function involved during donor loading in transfer development.

Still another object of the invention is to improve upon known transfer development processes.

SUMMARY OF THE INVENTION This invention is directed to an apparatus for developing a latent electrostatic image formed on an image retaining member. The apparatus includes a means for developing the latent image and this means includes: (a) a donor member adapted to transport toner particles to said said latent image comprising an endless member having a continuous, corona-chargeable dielectric surface; (b) means to continuously advance said donor member past a plurality of treating stations, said treating stations including: (1) a charging station located adjacent the surface of said donor member and including a charging means adapted to corona charge the surface of said donor member; (2) a toner loading station including a toner support member and a supply of toner particles supported thereby, said support member comprising a conductive material having on the toner-contacting surface thereof a material capable of triboelectrically charging said toner particles to a polarity opposite to that of the charge on the surface of said donor member; means for maintaining said conductive material at a lower potential than the charge on said donor member, said toner support member being located closely adjacent a portion of the periphery of the surface of said donor member, and a means to effect relative movement between said toner particles and said support member to charge said toner particles and fluidize said particles into contact with the surface of said donor member; and (3) a developing station including a rotatable latent electrostatic image bearing member positioned in developing relation with respect to the surface of said donor member.

The present invention is also directed to a method of developing a latent electrostatic image. The process includes forming a latent electrostatic image on the surface of an image-retaining surface, transporting the surface of a donor member, having a corona-chargeable dielectric surface, past a plurality of treating stations, said treating stations including, (1) a toner loading station comprising a supply of toner particles supported by a conductive support member which has on the toner-contacting surface thereof a material capable of triboelectrically charging said toner particles during relative motion therebetween, (2) a charging station including a charging means adapted to corona charge said dielectric surface; (3) a development station at which toner particles carried by said donor member are presented in developing relation to said latent image; maintaining said support member in close proximity to the periphery of said donor member; corona charging the surface of said donor member while vibrating said conductive support member so as to charge said toner particles and fiuidize the same into contact with said dielectric surface and while maintaining said conductive support member at a potential lower than the charge on said donor surface.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as other objects and further features thereof, reference is made to the accompanying drawing, wherein:

FIG. 1 is a sectional view of xerographic apparatus in accordance with the present invention; and

FIG. 2 is an enlarged cross sectional view of one portion of the donor member and toner loading station in accordance with the present invention.

DETAILED DESCRIPTION OF THE The present invention is a transfer development sys tem and method in which toner particles are applied to an electrostatic latent image on a latent electrostatic image retaining surface to develop the image. Although the system and method is described herein as part of a xerographic copier, it can be utilized in conjunction with any reproduction system wherein a latent electrostatic image is to be developed by applying toner thereto.

Referring to FIG. 1, there is shown a xerographic reproduction system utilizing the concept of the present invention. In this apparatus a xerographic plate is in the form of a drum 10 which passes through stations A-E in the direction shown by the arrow. The drum has a suitable photosensitive surface, such as one including selenium overlying a layer of conductive material, on which a latent electrostatic image can be formed. The various stations about the periphery of the drum which participate in the reproduction process are: charging station A, exposing station B, developing station C, transfer station D, and cleaning station E. Stations A, B, D, E represent more or less conventional means for carrying out their respective functions. Apart from their association with the novel arrangement to be described with respect to station C they form no part of the present invention.

At station A, a suitable charging means 12, e.g. a corotron, places a uniform electrostatic charge on the photoconductive material. As the drum rotates, a light pattern, via a suitable exposing apparatus 14, e.g. a projector, is exposed onto the charged surface of drum 10. The latent image thereby formed on the surface of the drum is developed or made visibly by the application of a finely divided pigmented resinous powder called toner, at developing station C, which is described in greater detail below. After the drum is developed at station C, it passes through transfer station D, comprising copy sheet 16, corona charging device 18 and fuser device 20. Following transfer and fixing of the developed image to the copy sheet, the drum rotates through cleaning station E, comprising cleaning device 22, e.g. a rotating brush.

At developing station C, the apparatus includes a donor member 24. Donor member 24 includes a grounded metal cylinder 26 carrying on the surface thereof a corona chargeable dielectric film 28-. The donor member is rotatably mounted adjacent a toner reservoir 32 which is more particularly described below. Reservoir 32 contains a supply of toner particles 34. The donor roll 2 f is located so as to provide a small gap between the surface of drum 10 and the outer surface of a toner layer carried by donor roll 24. This gap can be approximately l-10 mils. Donor roll 24 is adapted to be rotated in the direction shown by the arrow. Located adjacent the periphery of the donor roll 24 is a charging means 30 e.g. a corona charging device. This charging device is located between the toner reservoir 32 and the development region of the system and is adapted to corona charge the surface of donor roll 24 prior to its entry into the toner reservoir. Located adjacent the periphery of the donor roll 24 at a point between the toner reservoir 32 and the development region C of the system is a second charging device 38 eg, a corona charging device, which is adapted to impart a uniform charge to toner particles carried by the surface of the donor roll.

Following development, the donor roll is prepared for toner reloading by exposing the residual toner thereon to a neutralizing charging means 40, e.g. a corotron, to make easier the removal of the residual toner by way of a suitable cleaning means, e.g. a rotating brush 42, which may be equipped with a vacuum means not shown. The donor roll is thus freed of any image history or ghost image from the development region and is prepared to pick up a new supply of toner.

Referring now to FIG. 2 of the drawing, there is shown part of a donor member of the type contemplated by the present invention and its relationship with the toner reservoir 32. Toner reservoir 32 includes a conductive support member 44 having on the interior toner-contacting surface thereof material 46 which is capable of triboelectrically charging the toner particles to a polarity opposite to that of the charge on the surface of the donor member. The material selected as coating 46 should be such that when relative motion is created between this surface and toner particles supported thereby, a positive charge will be produced on the one material and a negative charge on the other. An example of such a material is polymerized methyl methacrylate known commercially as Lucite and manufactured by E. I. du Pont de Nemours & Company, Wilmington, Del. This material, when in frictional contact with a toner material such as carbon-pigmented, resinmodified phenolformaldehyde resin known commercially as Amberol F-71, manufactured by Rohm and Haas Company, the Resinous Products Division, Washington Square, Philadelphia, Pa., causes the toner to acquire a negative charge while it acquires a positive charge. Other suitable materials to be employed as coating 46 and as the toner particles herein are represented by those disclosed in US. Pat. 2,638,416. Conductive support member 44 is shown to be electrically grounded so that it is maintained at a lower charge potential than the corona charge placed onto dielectric surface 2 8 by corona charging means 30.

A vibrating means 36 is in association with toner reservoir 32 and is adapted to impart relative motion between the material 46 coated on the inside reservoir 32 and the toner particles. The degree of relative motion should be such that it will cause rubbing contact of the toner particles with material 46 and also to bring the toner particles into contact with the surface of donor member 24. As shown in FIG. 2 the toner is charged negative triboelectrically by virtue of its frictional contact with material 46 coated on the inside of the toner reservoir. Charging device 30 is shown depositing a positive charge onto the surface of dielectric layer 28. As the donor member rotates into the toner particles, the particles are attracted to the positively corona charged dielectric donor surface. In order that a uniform film of toner particles be deposited on the surface of the charged dielectric surface, it is necessary that the spacing between the dielectric surface and the conductive material of the toner reservoir be such that a field exists therebetween. This field must be strong enough so that toner particles will deposit on the surface of the charged dielectric. A spacing of from 2-70 mils between arrows a and b has been found appropriate when a voltage differential of about 300 volts exists between the two surfaces.

In operation, the toner reservoir is filled with an appropriate toner and the reservoir is vibrated via vibrating means 36. Next donor member 24 is rotated and a corona charge is applied to the surface thereof via charging means 30. The charged donor surface, as it reaches its lowest point in the reservoir, will attract toner particles to the surface thereof and these toner particles will be transported to the development region for development of the latent electrostatic image. In order to insure that the toner particles adhering to the donor surface are of uniform charge, charging device 38, e.g. a corona charging device, can apply a uniform charge to the layer of toner.

It is to be understood that While for purposes of illustration the donor member has been described basically as a cylinder, it may be an endless belt adapted to deliver toner from the toner source to the several stations. Conventional drive means, e.g. motors, belts, etc. are employed to drive the several movable members all in a manner well within the skill of the art.

Since many changes can be made in the above construction and many apparently widely different embodiments of this invention can be made without departing from the scope thereof, it is intended that all matter contained in the drawing and specification should be interpreted illustratively and not in a limited sense.

What is claimed is:

1. The method of developing a latent electrostatic image comprising forming a latent electrostatic image on the surface of an image-retaining surface, transporting an endless donor member, having a corona-chargeable dielectric surface on a conductive substrate, past a plurality of treating stations, said treating stations including, (1) a toner loading station comprising a toner support member and a supply of toner particles supported thereby, said support member being of a conductive material which has on the toner-contacting surface thereof a material capable of triboelectrically charging said toner particles during relative motion therebetween; (2) a charging station including a charging means adapted to corona charge said dielectric surface prior to its contact with toner particles; and (3) a development station at which toner particles carried by said donor member are presented in developing relation to said latent image; maintaining said toner support member in close proximity to the periphery of said donor member; maintaining said conductive substrate at a reference potential and uniformly corona charging the surface of said donor member while vibrating said conductive support member, so as to charge said toner particles and fluidize the same into contact with said dielectric surface, and while maintaining said conductive support member at a potential relative to the potential of the corona charged dielectric surface that establishes a toner-influencing field therebetween for loading toner onto the dielectric surface of the donor member.

2. The method of claim 1 including another charging station having a charging means which applies a uniform charge to toner particles adhering to the surface of said donor member.

References Cited UNITED STATES PATENTS 3,405,682 10/1968 King et al. 11717.5 3,357,399 12/1967 Fisher 117-17.5 3,393,663 7/1968 Donalies 117-l7.5 3,396,700 8/1969 Donalies l1717.5 3,460,468 8/1969 Johnson 11717.5 3,484,265 12/1969 Swyler l1717.5

WILLIAM D. MARTIN, Primary Examiner M. SOFOCLEOUS, Assistant Examiner US. Cl. X.R. 118-637 

